Lava erupting on sea floor linked to deep-carbon cycle

Date:

May 2, 2013

Source:

Smithsonian

Summary:

Scientists have found unsuspected linkages between the oxidation state of iron in volcanic rocks and variations in the chemistry of the deep Earth. Not only do the trends run counter to predictions from recent decades of study, they belie a role for carbon circulating in the deep Earth.

Share:

Total shares:

FULL STORY

Molten magma erupted onto the seafloor freezes to glass that contains clues to its origin in Earth's deep interior and ancient past (field of view ~1 cm). Volcanic glasses like this one may reveal a link between Earth's oxidation state and the deep carbon cycle.

Credit: Glenn Macpherson and Tim Gooding

Molten magma erupted onto the seafloor freezes to glass that contains clues to its origin in Earth's deep interior and ancient past (field of view ~1 cm). Volcanic glasses like this one may reveal a link between Earth's oxidation state and the deep carbon cycle.

Credit: Glenn Macpherson and Tim Gooding

Scientists from the Smithsonian and the University of Rhode Island have found unsuspected linkages between the oxidation state of iron in volcanic rocks and variations in the chemistry of the deep Earth. Not only do the trends run counter to predictions from recent decades of study, they belie a role for carbon circulating in the deep Earth.

The team's research was published May 2 in Science Express.

Elizabeth Cottrell, lead author and research geologist at the Smithsonian's National Museum of Natural History, and Katherine Kelley at the University of Rhode Island's Graduate School of Oceanography measured the oxidation state of iron, which is the amount of iron that has a 3+ versus a 2+ electronic charge, in bits of magma that froze to a glass when they hit the freezing waters and crushing pressures of the sea floor. Due to the high precision afforded by the spectroscopic technique they used, the researchers found very subtle variations in the iron-oxidation state that had been overlooked by previous investigations.

The variations correlate with what Cottrell described as the "fingerprints" of the deep Earth rocks that melted to produce the lavas -- but not in the way previous researchers had predicted. The erupted lavas that have lower concentrations of 3+ iron also have higher concentrations of elements such as barium, thorium, rubidium and lanthanum, that concentrate in the lavas, rather than staying in their deep Earth home. More importantly, the oxidation state of iron also correlates with elements that became enriched in lavas long ago, and now, after billions of years, show elevated ratios of radiogenic isotopes. Because radiogenic isotopic ratios cannot be modified during rock melting and eruption, Cottrell called this "a dead ringer for the source of the melt itself."

Carbon is one of the "geochemical goodies" that tends to become enriched in the lava when rocks melt. "Despite is importance to life on this planet, carbon is a really tricky element to get a handle on in melts from the deep Earth," said Cottrell. "That is because carbon also volatilizes and is lost to the ocean waters such that it can't easily be quantified in the lavas themselves. As humans we are very focused on what we see up here on the surface. Most people probably don't recognize that the vast majority of carbon -- the backbone of all life -- is located in the deep Earth, below the surface -- maybe even 90 percent of it."

The rocks that the team analyzed that were reduced also showed a greater influence of having melted in the presence of carbon than those that were oxidized. "And this makes sense because for every atom of carbon present at depth it has to steal oxygen away from iron as it ascends toward the surface," said Cottrell. This is because carbon is not associated with oxygen at depth, it exists on its own, like in the mineral diamond. But by the time carbon erupts in lava, it is surrounded by oxygen. In this way, concludes Cottrell, "carbon provides both a mechanism to reduce the iron and also a reasonable explanation for why these reduced lavas are enriched in ways we might expect from melting a carbon-bearing rock."

Story Source:

The above post is reprinted from materials provided by Smithsonian. Note: Materials may be edited for content and length.

July 31, 2015  Resettlement projects in the Amazon are driving severe tropical deforestation, according to new research. Widely hailed as a socially responsible and 'innocuous' strategy of land redistribution, ... read more

July 31, 2015  The humble butterfly could hold the key to unlocking new techniques to make solar energy cheaper and more efficient, pioneering new research has shown. By mimicking the v-shaped posture adopted by ... read more

July 30, 2015  China needs to reduce its dependence on coal and improve the range of fuels it uses if it is to have long term energy security, according to new research. The study looks at the future of electricity ... read more

July 30, 2015  North of the Aleutian Islands, submarine canyons in the cold waters of the eastern Bering Sea contain a highly productive 'green belt' that is home to deep-water corals as ... read more

July 30, 2015  New findings have implications for questions regarding how animals and plants grow minerals into shapes that have no relation to their original crystal symmetry, and why some ... read more

July 30, 2015  A new study addresses an important question in climate science: how accurate are climate model projections? Climate models are used to estimate future global warming, and their accuracy can be ... read more

June 19, 2015  Over billions of years, the total carbon content of the outer part of the Earth -- in its mantle lithosphere, crust, oceans, and atmospheres -- has gradually increased, scientists say. The new ... read more

Mar. 28, 2011  Most deep-sea volcanoes produce effusive lava flows rather than explosive eruptions, both because the levels of magmatic gas tend to be low, and because the volcanoes are under a lot of pressure from ... read more